1. Field of the Invention
The present invention relates to disease detecting means for human eyes and more particularly to inspection instruments for human crystalline lenses. More specifically, the present invention pertains to an inspection instrument which makes possible observations of optical sections of a crystalline lens as well as observations under a retroillumination method so that cataract and its progress can readily be detected.
2. Description of the Prior Art
Conventional eye disease inspection instruments include a crystalline section observation instrument in which a thin planar pattern of light or a so-called slit light is projected through a crystalline lens and the illuminated section of the crystalline lens is observed in a direction having an angle with respect to the illuminated section. It has also been known to arrange the image plane of the observation optical system so that an extension of the image plane contains a line of intersection between the plane of the slit light and a principal plane of the imaging optical system of the observation optical system. With this optical arrangement, it becomes possible to have the crystalline section image focused throughout the section and an example of such optical arrangement is disclosed for public inspection on Sept. 9, 1978 by Japanese Patent Public Disclosure No. 53-103686 corresponding to Patent Application No. 52-18511, filed on Feb. 21, 1977. The conventional instrument is considered as being advantageous in that the image of the crystalline section can be performed in a focused condition throughout the section. However, inconveniences have been encountered in that each observation can be performed with respect to one section only so that a lot of time is required to perform observations throughout the eye. Thus, the conventional instruments have been very inconvenient in making an accurate judgement of the location and the progress of the disease in an inspection of, for example, cataract.
As a method for observing an overall image of a crystalline lens, it has been known to project a slit light to a patient's eye and illuminate the crystalline lens by light beams which are reflections at the eye fundus of the projected slit light. The method is known as a retroillumination from an eye fundus and an instrument for performing the retroillumination method may include a polarizer in the illuminating optical system and an analyzer in the observing optical system. Examples of such optical arrangement are disclosed in Japanese publications "Rinsho Ganka (Clinical Ophthalmology)" Vol. 32, No. 6 (June 1978) and "Nippon Ganka Gakkai Zasshi (Japan Ophthalmologic Institute Journal)", Vol. 62, No. 4, Apr. 10, 1958, page 22-(380)-26(384). It has however been recognized that the conventional instrument for the retroillumination method cannot be used for the purpose of recording and measurement, since assurance cannot be made in respect of stabilities of direction of the slit illumination beams, of the quantity of illumination light, of the direction of observation and of the position of observation.